Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $76.49   9.634%   $83.859   $83.86   $83.85   $83.90  
  Purchase #2 $61.39   12.171%   $68.8618   $68.86   $68.85   $68.90  
  Purchase #3 $26.66   3.697%   $27.6456   $27.65   $27.65   $27.60  
  Purchase #4 $169.44   3.766%   $175.8211   $175.82   $175.80   $175.80  
  Purchase #5 $194.59   6.576%   $207.3862   $207.39   $207.40   $207.40  
  Purchase #6 $182.87   8.548%   $198.5017   $198.50   $198.50   $198.50  
  Purchase #7 $9.80   7.664%   $10.5511   $10.55   $10.55   $10.60  
  7 purchase totals = $721.24       $772.6265   $772.63   $772.60   $772.70